Recently, interests in energy storage technologies have been increasingly grown, and efforts for the development of high-capacity electrochemical devices have been gradually materialized as the application of the energy storage technologies is expanded to mobile phones, camcorders, notebook PCs, and even to electric vehicles.
There emerges an interest in rechargeable secondary batteries among these electrochemical devices, and, particularly, lithium secondary batteries developed in the early 1990's are spotlighted because the lithium secondary batteries are advantageous in that they have higher operating voltage and significantly higher energy density.
A lithium secondary battery is composed of a carbon negative electrode capable of intercalating and deintercalating lithium ions, a positive electrode formed of a lithium-containing composite oxide, and a non-aqueous electrolyte solution in which a lithium salt is dissolved in a mixed organic solvent.
In the lithium secondary battery, lithium ions react with the electrolyte solution in a voltage range of 0.5 V to 3.5 V during initial charge to form compounds, such as Li2CO3, Li2O, and LiOH, and a solid electrolyte interface (SEI), as a kind of a passivation layer, is formed on the surface of the negative electrode by these compounds.
The SEI film formed at an initial stage of charging may prevent a reaction of the lithium ions with the carbon negative electrode or other materials during charge and discharge. Also, the SEI film may only pass the lithium ions by acting as an ion tunnel. Since the ion tunnel may prevent the destruction of a structure of the carbon negative electrode due to the co-intercalation of the carbon negative electrode and the non-aqueous organic solvents having a high molecular weight which solvate lithium ions and moves therewith, cycle life characteristics and output characteristics of the lithium secondary battery may be improved.
In a case in which the organic solvent used in the non-aqueous electrolyte solution of the lithium secondary battery is generally stored for a long period of time at high temperature, gas is generated due to the occurrence of a side reaction of the organic solvent with a transition metal oxide of a discharged positive electrode active material. Furthermore, the negative electrode is exposed while the SEI film is gradually collapsed during high-temperature storage in a fully charged state (e.g., storage at 60° C. after charged to 100% at 4.2 V), and the exposed negative electrode continuously reacts with the electrolyte solution to generate gases, such as CO, CO2, CH4, and C2H6.
Battery swelling and deformation of an electrode assembly occur while an internal pressure of the battery is increased by the gas thus generated, and, as a result, the battery may be deteriorated due to internal short circuit of the battery, or fire or explosion of the battery may occur.
In order to address these limitations, there is a need to develop an electrolyte solution for a lithium secondary battery which may suppress the side reaction during high-temperature storage.
Priot Art Documents
Japanese Patent Application Laid-open Publication No. 2010-116475